While working on #660 (http://trac.navit-project.org/ticket/660#comment:50
) to improve Navit's decisions on whether or not to announce a maneuver, I came across one case in which the decision requires information currently not supported by Navit: the number of lanes a street has.
This should not be too hard to add to Maptool (it would be one additional attribute), but I would like to hear some opinions on this.
Background: I assume that on a motorway most drivers don't want announcements telling them not
to take the next exit but continue on the motorway. The only two maneuvers needed when traveling on a motorway are exits we need to take, and which lane to take at motorway interchanges.
The latter is problematic at various type of interchanges at which exactly one way is mapped as motorway while all others are mapped as ramps: For Navit this is indistinguishable from a regular exitm, therefore following the way mapped as morotway generates no announcement. In the real world, however, it is not always clear for the driver which road is the right one.
All of this is easy when more than one way is mapped as a motorway: these cases are easy to identify and Navit will (as of r5938) announce the maneuver. The problematic cases are those where only one way is mapped as a motorway.
The only heuristic to tell an interchange from a regular exit would be to count the number of lanes: if the ramp has at least as many lanes as the motorway, then it is likely to be an interchange. I have come across two cases (documented in the ticket) where this heuristic would solve the issue.
So – should we implement support for lanes in maptool?